1. Field of the Invention
The present general inventive concept relates to a spatial sound system, and more particularly, to a spatial sound generation method and apparatus by which reflected sounds of an input sound signal are generated, and by using the reflected sounds, a spatial sound is generated.
2. Description of the Related Art
Generally, a spatial sound generation apparatus creates a virtual sound source at a predetermined position of a virtual room through headphones or speakers disposed at predetermined locations, and generates a direction effect, a distance effect, and a spatial effect, to make it appear as if the sound that a listener listens to comes from the virtual sound source. For example, the spatial sound generation apparatus generates a spatial sound signal by using reflected sounds, so that the listener can experience a spatial effect and spatial effect through 2-channel headphones, earphones, or speakers.
FIG. 1 is an echogram illustrating a conventional method of generating a reflected sound.
Referring to FIG. 1, the echogram includes a direct sound (non-reflected sound), an early reflected sound, and a late reflected sound (reverberation sound).
The early reflected sound usually uses a tapped delay line method with a tapped delay line including a delay filter and multipliers. The tapped delay line method performs a type of finite impulse response (FIR) filtering, and requires tens to hundreds of delay filters, multipliers, and adders in order to generate tens to hundreds of early reflected sounds.
Also, the late reflected sound is artificially generated by using a Schroeder reverberator as illustrated in FIG. 2. The Schroeder reverberator is mentioned in U.S. Pat. No. 5,491,754, titled “Method and System for Artificial Spatialisation of Digital Audio Signals,” and filed on Feb. 19, 2003.
This Schroeder reverberator includes four parallel-connected feedback comb filters and two serially-connected all-pass filters. An input sound signal x(z) is transferred in parallel through the four feedback comb filters, which have different delay values and gain values, and then added up and output. The added outputs of the four feedback comb filters are transferred through the two serially connected all-pass filters having different delay values and gain values to generate reflected sounds. Finally, the signal passing through the two all-pass filters is output as a sound signal y(z) having a spatial effect.
However, since the Schroeder reverberator does not provide positioning of the reflected sounds, the Schroeder reverberator does not consider directivity, and thus cannot produce sounds that are perceived by a listener to be directional, and is limited at least with respect to generating an accurate virtual spatial sound.
Accordingly, the conventional method of generating a spatial sound using reflected sounds requires a very large amount of computation due to a separate use of the tapped delay line and the artificial reverberator, and does not provide positioning of reflection sound sources.
Besides the conventional technology described above, there are methods using a Head Related Transfer Function (HRTF) in order to generate a more accurate spatial sound.
However, since these methods using the HRTF require a very large amount of computation, they are not suitable for portable sound devices.